The most persistent feature of severe obesity in man and animals is an excess number of fat cells (adipocytes). The proposed studies will determine nutritional, metabolic, and cellular events which relate to the production of excess fat cells in the rat. We will examine the effects of various diets on hyperplastic adipose tissue growth to determine whether some nutrients are particularly important in the promotion of such growth. We will compare the metabolism of rats given different stimuli to induce hyperplasia (diet and cold exposure) and thereby elucidate aspects of metabolism central to the phenomenon. We will study the association between the morphologic features of obesity and metabolic disorders such as hyperinsulinemia. We propose to study the cellular basis of induced fat cell production in the rat via an examination of the fate of isotopic labeled DNA precursors in various models of obesity; in particular, uptake of label in adipose tissue in rats induced to hypertrophic-hyperplastic obesity will be compared to uptake in rats induced to hypertrophic, non-hyperplastic obesity. The recently described phenomenon of accelerated uptake of label in vitro by adipose tissue fragments from pre-hyperplastic rats will be scrutinized to determine whether it is an accurate predictor of impending hyperplasia in both man and animals.